Recently, high integration and miniaturization of semiconductors widely used in electronic equipment, communication devices, personal computers and the like have been more and more rapidly progressed. Under such circumstances, various characteristics required of a laminate for a semiconductor package to be included in a printed circuit board have become more and more severe. The required characteristics are characteristics such as low water absorption, heat resistance after moisture absorption, flame retardancy, a low dielectric constant, a low dielectric loss tangent, a small coefficient of thermal expansion, heat resistance and chemical resistance. These characteristic requirements have been, however, not necessarily satisfied yet.
Cyanate ester compounds have been conventionally known as resins for a printed circuit board having excellent heat resistance and electric characteristics, and resin compositions using a bisphenol A-based cyanate ester compound and another thermosetting resin or the like have been widely used as, for example, materials of printed circuit boards. A bisphenol A-based cyanate ester compound is excellent in the electric characteristic, mechanical characteristic, chemical resistance characteristic and the like. The cyanate ester compound is, however, sometimes insufficient in low water absorption, heat resistance after moisture absorption, flame retardancy and heat resistance. Therefore, for purpose of further improving various characteristics, examinations have been made on a variety of cyanate ester compounds having different structures.
As a resin having a different structure from the bisphenol A-based cyanate ester compound, for example, a novolac-based cyanate ester compound is often used (see Patent Document 1). The novolac-based cyanate ester compound has, however, the following problems: the compound is liable to be insufficiently cured, and a resultant cured product has high water absorption, which results in low heat resistance after moisture absorption. Therefore, as a method for solving these problems, prepolymerization of a novolac-based cyanate ester compound and a bisphenol A-based cyanate ester compound has been proposed (see Patent Document 2).
Besides, as a method for improving the flame retardancy, it has been proposed that a halogen-based compound is contained in a resin composition by, for example, using a fluorinated cyanate ester compound, or mixing or prepolymerizing a cyanate ester compound with the halogen-based compound (see Patent Documents 3 and 4).